1. Field of the Invention
The present invention relates to a circuit which limits the maximum amplitudes of signals outputted from a differential output circuit employed in an integrated circuit to arbitrary amplitude values respectively.
2. Description of the Related Art
There has heretofore been known an amplitude voltage limiting circuit simple in configuration, using transistors of so-called “diode connection” wherein the gates and drains of such transistors 40 and 42 as shown in FIG. 1 are respectively connected to one another in an analog circuit having differential outputs symmetric and equal to a center voltage. It is well known that the amplitudes of output signals Outp and Outn are limited by threshold voltages Vth of the transistors in the present circuit.
On the other hand, a patent document (Japanese Unexamined Patent Publication No. 2001-127566) has disclosed an example illustrative of both the detection of the peaks of analog signals by using a differential circuit and a source follower circuit and an amplitude detecting circuit using the same.
However, the amplitude limiting circuit shown in FIG. 1 has the problem that a limiting voltage is limited by the threshold value Vth of each transistor, corresponding to a process parameter and hence a designer encounters difficulties in setting it to a desired value. Since the threshold value Vth remains unchanged even if, for example, the gate widths and the gate lengths of the diode-connected transistors are changed, it was difficult to set the limiting voltage to an arbitrary value desired by the circuit designer. Further, the amplitude liming circuit has a drawback in that since the threshold value Vth of each transistor depends on the temperature, an amplitude limiting voltage changes depending on the temperature.